This toolbar enables you to modify subtitles by splitting, joining, moving rows between subtitles, moving words among lines, edit subtitle numbers and comments, etc.
All of these commands can be found in the Subtitles menu and its submenus.
Show subtitle's ID/Number editor. SubtitleNEXT allows any text to be used as a subtitle ID, not only numbers. If you want to stick to consecutive numbers as subtitle IDs, you can set Auto Renumber option in the Preferences.